Solid-State Switches
Various solid-state switches, such as PIN diodes and FETs, are known in the art. Such switches often have as limitations slow switch speeds (i.e., switching speed in the GHz range), low isolation in the OFF state (for example, less than 10 dB at 10 GHz), high insertion loss in the ON state (for example, greater than 1 dB at 10 GHz), a large footprint (for example, several mm2), a requirement for high power to operate the switch, the ability to perform switching only as binary state switching devices (e.g., “on” or “off” representing only two states such as “0” and “1”), and the possibility of accomplishing multi-throw switching by staggering an array of binary switches. In fact, such a multi-throw switching capability comes at the cost of increasing the on-chip real-estate and is counter to current trends in the electronics industry towards ultimate miniaturization.
MEMS Switches
Microelectromechanical system (hereinafter “MEMS”) switches are also known in the art. MEMS switch speeds have been reported to be in the range of approximately 10 to 100 μsec, but can be as low as 1 μsec with increased actuation voltage applied to the switch. Relative to solid state switches, MEMS switches can offer improved isolation, improved insertion loss, smaller size (such as a 1000 μm2 footprint), and lower power dissipation (for example, a few μW). However, it is common that MEMS switches require high actuation voltages (for example, approximately 30V to 80V), and can be operated only by using high-voltage drive chips. In addition, conventional MEMS switches appear to have a cyclability problem, which may be associated with fatigue-related failure, for example caused by thermally induced stress in bimporph structures. The same problem with multi-throw switching that was described for solid state switches applies equally to MEMS switches.
NEMS Switches
Nanoelectromechanical system (hereinafter “NEMS”) switches are also known in the art. NEMS switches depend in part on the material properties of carbon nanotubes (hereinafter “CNT” or “CNTs”). CNTs have very interesting properties because of their chemical composition (based on pure carbon), chemical bonding and mechanical structure. CNTs can be used in conventional NEMS switches by taking advantage of such properties as ultra-low low mass, high directional stiffness (for example, an elastic modulus of approximately 1 TPa), high inductance (16 nH/μm), low capacitance, and the ability to operate using electrostatic actuation. Conventional NEMS switches can produce ultra-high switch speeds, high isolation, low insertion loss, ultra-small size, ultra-low power dissipation, low actuation voltages, and long cyclability. In addition, nanotube-based NEMS have been demonstrated in applications involving nanotweezers, memory devices, supersensitive sensors, and tunable oscillators. Nanorelays are another promising application of nanotubes that offer the potential for high-performance switching, with high-speed operation at low actuation voltages and power.
Electromechanical switching in CNTs was first observed in devices in which single-walled nanotubes (hereinafter “SWNT” or “SWNTs”) were mechanically manipulated to form crossed nanotubes with an air gap (that is, a crossed orientation of nanotubes that form a point contact when brought together). Others have demonstrated switching in deposited multiwalled nanotube (hereinafter “MWNT” or “MWNTs”) cantilever structures, which were fabricated using an AC electrophoresis technique. Still others have also observed switching in devices using deposited MWNTs, where the individual tubes were located by SEM for subsequent e-beam and thin-film processing. Still others have demonstrated switching in deposited MWNTs cantilever devices using a technique that allows the air gap to be controlled to within 1 nm precision. Switching in both SWNTs and MWNTs has been reported for the case of deposited tubes. Nanotubes have previously been grown or deposited across trenches on a Si wafer, or been spun across the trenches at room temperature.
There is a need for switching systems that can provide the high speed operation associated with NEMS switches, with the added operational capabilities of operating at elevated temperatures and of providing convenient multi-throw (or multi-state memory) operation.